Bottom Line: Overeating Boosts Fat, Whatever the Protein Level

Overeating, Protein, & Weight Gain: Study Results continued...

The results: All groups gained weight, as expected. The low-protein group gained the least, about 7 pounds. The normal-protein group gained 13.3 pounds. And the high-protein group gained 14.4 pounds.

But "the low-protein group stored a higher percentage of calories as fat than the other groups," Bray tells WebMD.

In addition, the low-protein group lost lean body mass, about 1.5 pounds. The normal-protein group gained 6.3 pounds of lean body mass, and the high-protein group gained 7 pounds of lean body mass. Also, the calories burned while at rest increased in the normal- and high-protein groups, but not in the low-protein group.

While excess body fat is linked with obesity, increased lean muscle mass has a positive effect on metabolism.

Overeating & Protein Intake: Lessons

"The low-protein diet was clearly not good in terms of preserving lean body mass," Bray says.

The researchers did not find much difference in terms of body composition changes between the 15% or the 25% protein diet, Bray says.

"Based on the study, healthy adults should consider getting 12% to 15% protein [from their diet]," Bray says. (That recommendation does not apply to the elderly or athletes, he says, who may need more.)

For a 2,000-calorie diet, that level would mean taking in about 300 calories or 75 grams of protein daily. (A gram of protein has 4 calories.) A 3-ounce skinless chicken breast has about 27 grams of protein. Six ounces of Greek yogurt has about 14 grams.

Bray serves as a consultant for Abbott Laboratories and Takeda Global Research Institute. He is an advisor to Medifast, Herbalife, and Global Direction in Medicine. He has received royalties for the Handbook of Obesity.

The study results suggest the downsides of eating too little protein, says David Heber, MD, professor of medicine at the UCLA David Geffen School of Medicine and founding director of UCLA's Center for Human Nutrition. He co-authored an editorial to accompany the study.

"The danger of eating low protein is you eat too many refined carbohydrates," he tells WebMD. White bread, for instance, is a refined carbohydrate. "That puts on weight. And that weight tends to be fat."